On Aug 23, 6:43 pm, [EMAIL PROTECTED] wrote: > castironpi napisa³(a): > > > Is there a way to initialize a ctypes Structure to point to an offset > > into a buffer? I don't know if the way I'm doing it is supported. > > There is a high probability you're abusing ctypes too much, but it's > possible. The following seems to work: > > from ctypes import * > > class S(Structure): > _fields_ = [('x', c_uint), ('y', c_int)] > rawdata = create_string_buffer('\xEE\xFF\x78\x56\x34\x12\xFF\xFF\xFF > \xFF\xAA') > > # Try to make a structure s of type S which takes its data from > rawdata > # buffer, starting at index 2 > s = cast(c_void_p(addressof(rawdata)+2), POINTER(S)).contents > > print hex(s.x), s.y # Should be 12345678h and -1
Output is 0x12345678L -1, as you state. I understand that '\xEE\xFF' is skipped with addressof(rawdata)+ 2, which makes +2 an offset into the buffer. At this point, I'd say the use of 'cast' is dubious, but possible to support. My problem comes in, in that the buffer I have comes from a non-ctypes source. It is a, <drumroll please> mmap. My goals in exploring this are persistence and IPC, which are certainly not abusing Python too much. 'ctypes' may not be right for the job though. The solution I looked at got even worse than 'from _ctypes import _cast_addr'. I want a supported way to do it. -- http://mail.python.org/mailman/listinfo/python-list